1. Field of the Invention
The present invention relates to a device for feeding a recording sheet at a certain speed with high precision, preventing exposure unevenness caused by curl of the recording sheet.
2. Background Arts
In a printer processor, for instance, linear recording light beams are applied to a recording area of a photosensitive recording sheet in a main scan direction while the recording sheet is fed in a sub-scan direction perpendicular to the main scan direction, to record an image. Along a passage of the recording sheet are provided a plurality of feeding roller pairs, each of which transfers the recording sheet to the next one. In the vicinity of a record position to which the recording light beams are applied, the recording sheet is nipped by a first feeding roller pair, fed toward the record position, and transferred to a second feeding roller pair. These feeding roller pairs are controlled to be equal in the feeding speed.
Each of the first and second feeding roller pairs has a capstan roller and pinch roller which are located below and above the feeding passage of the recording sheet. Each of the capstan roller and the pinch roller has plural orbital grooves along an axial direction thereof, to divide outer surfaces of the capstan and the pinch rollers into plural roller bodies. The recording sheet is pressed by these roller bodies which is separated in the main scan direction, so it is possible to relax the strain or the deformation of the recording sheet with respect to the widthwise direction (main scan direction). Moreover, it is possible to prevent a crease in the recording sheet. Furthermore, the recording sheet is kept at a certain position with high accuracy with respect to the main scan direction, even when the recording sheet is completely passed the feeding roller pair, to prevent deviation in recorded position of the recording sheet.
On the other hand, the recording surface of the recording sheet is not entirely flat, but is curled in the widthwise or lengthwise direction. The recording area is not bent when the recording sheet is nipped and fed by the first and second feeding rollers. When passing the first feeding roller pair, however, the trailing end of the recording sheet is bent upward or downward, which causes deviation in exposed position. In that case, density unevenness in the recording sheet could be occurred. Moreover, before passing the second feeding roller pair, the leading end of the recording sheet is curled, so there is a possibility to occur density unevenness in a print image, as mentioned above.
In order to prevent bending of the recording sheet, it is preferable to position the recording sheet such that the both lateral ends thereof are come in contact with the roller bodies. However, this condition is depended upon width of the recording sheet. When positioned between the roller bodies, the both lateral ends of the recording sheet is curled, which causes exposure unevenness, as set above. In addition, a roller with no orbital grooves may be applicable for preventing the curl of the recording sheet. But in that case, strain or deformation in the main scan direction may be occurred, as described above.
In view of the foregoing, an object of the present invention is to provide a device for feeding a recording sheet capable of r educing strain and curl of the recording sheet effectively.
To achieve the above objects, a device for feeding a recording sheet comprises a first feeding roller pair having a first pinch roller and a first capstan roller, a second feeding roller pair having a second pinch roller and a second capstan roller, an d a plurality of orbital grooves formed in an outer surface of the second pinch roller and arranged in an axial direction of the second pinch roller. The depth of the orbital grooves is within a range of 0.2 mm to 0.7 mm.
In the preferred embodiment, the first pinch roller has a plurality of orbital grooves in an outer surface thereof, and the depth of the orbital grooves is within a range of 0.2 mm to 0.7 mm, in the same way as those of the second pinch roller. The first and second capstan rollers also have a plurality of orbital grooves, which are confronted with the orbital grooves of the corresponding pinch roller. The depth of the orbital grooves of the capstan rollers is set to 1.0 mm.
The capstan rollers and the pinch rollers are covered with elastic members, such as silicon rubbers. Between the first and second capstan rollers is disposed a guide member which has a guiding surface for supporting the recording sheet. The guiding surface is located to be 0.01 mm to 0.08 mm lower than the top level of the first and second capstan rollers. When the recording sheet is nipped by the feeding roller pair, the elastic member of the capstan roller is deformed such that the top level of the capstan roller becomes the same level as the guiding surface. Moreover, the guide member has plural guiding projections extended in a feeing direction of the recording sheet. The guiding projections are tapered off and fit into the orbital grooves of the capstan rollers. This ensures smooth conveyance of the recording sheet.
According to the present invention, the orbital grooves of the pinch rollers, shallower than those of the capstan rollers, are able to relax the strain of the recording sheet in the widthwise direction, and to suppress the curls of the recording sheet. Since the recording sheet is not deviated from the proper position, recording light beams from a recording device are applied to proper positions on the recording sheet, so exposure unevenness in the recording sheet can be prevented.